1. Field of Invention
The importance of high quality protein in human diets has long been recognized, but until recent years, animal protein was the main source of protein and was plentiful and relatively inexpensive. The recent world protein crisis has renewed interest in vegetable protein such as that found in vegetable seeds, nuts and legumes; particularly in view of the inefficient biological conversion of plant protein to animal protein. In the past, various processes were used for extracting oil from vegetable seeds, nuts, legumes and the like oil seeds but little attention had been given to the remaining vegetable proteins.
2. Prior Art
Oil seeds containing at least 30% oil have been processed for many years with the major interest being the removal of the oil, while regarding the proteinaceous material as by-product. It is to be understood throughout the specification and claims that the expression oil seeds is used in its broadest sense to include those substances known to the art that contain at least 30% oil. Basically the oil is removed by a process which includes cooking, pressing and then extracting the press cake to obtain the desired oil, the remaining proteinaceous material being treated as by-product. For example, it is well known that peanuts are a good source of protein and fat. However, prior methods of processing peanuts have emphasized efficient removal of the oil disregarding the proteinaceous fraction. In fact, some of the processing steps utilized to remove the oil severely damages or destroys functional properties of the remaining protein and renders it unfit or unsatisfactory for subsequent use in numerous food applications. Such functional properties of the protein which are damaged include water solubility, gelling properties and the like.
Conventional processes for removal of oil from oil seeds with greater than 30% oil, such as peanuts, specify extensive cooking, screw pressing followed by solvent extraction. The resulting protein meal product from such a process has low protein solubility, a tan to brown color, and a cooked flavor, all of which makes the product unsuitable for food applications such as use in dietetic drinks and the like where good water solubility is essential. The importance of flavor, while somewhat subjective, cannot be overlooked since, even if a protein has all the desirable properties except for acceptable flavor then its use as an edible food will be severely limited.
In order to improve the yield of oil and the quality of remaining protein various attempts have been made to alter the basic steps of cooking, pressing and extracting the oil from oil bearing seeds and nuts. One such approach is that which is disclosed in the patent to Drenning, U.S. Pat. No. 2,629,722 wherein it is taught that if best results are to be achieved in oil and meal production then the moisture content of the cooked seeds must be closely controlled, evaporation prevented, and the time and temperature of the cooking reduced. Thus, a process is disclosed in which oil bearing seeds and nut meats are first flaked and then treated prior to extraction of the oil by raising the moisture content of the meats to a value of between 12 and 20% by the addition of steam or water and then cooking the meats for a period of time between 7 and 20 minutes at a temperature between 190.degree. F. and 215.degree. F. under such conditions as to insure that evaporation does not reduce the moisture in the seed nut meats below 12%. The oil may then be extracted from the treated (cooked) seed by a combined process involving mechanized presure followed by solvent extractions. This process is said, among others, to produce a meal of high nutritional value above that obtained from a standard high temperature processing and to achieve higher oil yields. The process was specifically applied to cottonseed meats.
Various modifications of the basic process to facilitate solvent extraction of the oil from oil seeds are known as described in the patents to Gastrock et al, U.S. Pat. Nos. 2,726,253 and 2,727,914 and the patent to Jones et al, U.S. Pat. No. 3,347,885.
The first Gastrock et al patent is directed to a process of preparing oil bearing materials for solvent extraction, which comprises subjecting the unpressed flakes to a mild heat treatment sufficient to make the oil easily extractable but insufficient to seriously damage protein; combined with a crisping treatment, which is a partially dehydrative cooling of the cooked materials, lowering moisture by 2-4%, that converts them to relatively porous and incompressible granules. The thus treated flakes are then countercurrently mixed with separate portions of solvents, and residual solids are removed from each portion of solvent by means of extraction. The process is said to be advantageously used in the solvent extraction of oil from oil bearing seeds having a relatively high oil content, such as cottonseeds, peanuts, sesame, flaxseed, babassu nuts, and the like.
The second Gastrock et al patent describes the solvent extraction of rice bran oil from rice bran in which the rice bran particles are subject to a mild cooking at a moisture level of at least 14% at the early stages, and then the moisture content is allowed to drop in the latter stages of cooking to from 6 to 18% while the cooking temperature is increased from about 170.degree. and 210.degree. F. in the early stage to about 235.degree. F. in the final stage. The cooked rice bran particles are then made crisp by exposure to a relatively cool atmosphere conducive to the evaporation of moisture until they undergo a substantially uniform decrease in temperature to below 130.degree. F. and a substantially uniform loss of moisture sufficient to lower their moisture content by from about 2 to 4%. Finally, the resultant cooked and crisped rice bran particles without flaking, are mixed with a solvent for a rice bran oil to remove the oil.
The Jones et al patent relates to a direct extraction of oil and is said to be an improvement on the Gastrock et al process by providing a method for directly solvent extracting cooked cottonseed meat particles by gravity flow or percolation while eliminating the necessity of pre-pressing mildly cooked cottonseed particles. The result is obtained by maintaining a moisture content of from 13 to 14%.
Thus, as can be seen various techniques have been developed to remove oil from oil seed while retaining adequate properties of the remaining protein. However, a completely efficient and effective method of extraction has not yet been achieved in which oil seeds and the like are solvent extracted to provide a proteinaceous material having good functional properties and wide applicability in various food applications.